The ability to regulate cellular processes at the genetic level in a highly selective and therapeutic manner is now offered by various forms of oligonucleotide-based pharmaceuticals. These oligonucleotides are designed according to their nucleic acid sequence to arrest genetic processes by binding disruptively to a selected genetic target, usually a viral gene or a human gene that is associated with a particular disease state such as cancer or a condition such as inflammation. Transcription of an undesired gene can, for example, be arrested by a synthetic oligonucleotide that hybridizes selectively to a control region or coding region of that gene; similarly, translation of an undesired protein can be arrested using an oligonucleotide that hybridizes with a control region or coding region of the messenger RNA encoding that protein. Many of the problems associated with the practical use of such oligonucleotide-based therapeutics, such as cell uptake, stability, and cost of production, have been resolved by recent advances in nucleic acid chemistry.
These current strategies contemplate principally the use of oligonucleotides which, in order to hybridize to their intended nucleic acid target, are necessarily single-stranded complements of that target. That is, oligonucleotides intended for use as pharmaceuticals are designed currently to bind as single-stranded entities to other nucleic acid targets, whether single-stranded messenger RNA or single stranded DNA (the so-called "sense" and "anti-sense" approaches, reviewed for example by Uhlmann et al., 1990, Chemical Rev., 90:543) or, as has more recently been proposed, to double stranded DNA (the "triplex" approach). These approaches neglect other cellular targets that are at least equally attractive in the overall development of gene regulating therapeutics. More particularly, it would be desirable to provide oligonucleotide agents capable of interfering with interactions specifically between nucleic acids and their ligands, particularly their protein ligands, which play a role in infectious and other disease states.
The feasibility of designing oligonucleotides that interfere with a protein/nucleic acid interaction of therapeutic interest is complicated in that, in the majority of instances, the protein recognizes a nucleic acid that is double-stranded in structure; and further in that double stranded oligonucleotides of the small size necessary for pharmaceutical applications, for uptake by the cell, and for stability, are highly unstable and must typically be incubated under temperatures so cold and/or salt concentrations so high as to make subsequent study and use of the duplexed structures impractical.
It is a principle object of the present invention to provide polynucleotide conjugates that are capable of adopting a ligand-binding duplexed structure which has enhanced stability, i.e. enhanced physical or chemical stability.
A further object of the present invention is to provide stability-enhanced duplexed polynucleotide conjugates having anti-viral activity.